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XJDIES ON FUSARIUM DISEASES OF 
POTATOES AND TRUCK CROPS 
IN MINNESOTA 



A THESIS SUBMITTED TO THE FACULTY 

OF 

THE GRADUATE SCHOOL 

OF 

THE UNIVERSITY OF MINNESOTA 

BY 

G. R. BISBY 

IN PARTIAL FULFILMENT s OF THE REQUIREMENTS 

FOR THE DEGREE OF 

DOCTOR OF PHILOSOPHY 

JUNE 1918 



STUDIES ON FUSARIUM DISEASES OF 

POTATOES AND TRUCK CROPS 

IN MINNESOTA 



A THESIS SUBMITTED TO THE FACULTY 

OF 

THE GRADUATE SCHOOL 

OF 

THE UNIVERSITY OF MINNESOTA 

BY 

G. R. BISBY 

IN PARTIAL FULFILMENT OF THE REQUIREMENTS 

FOR THE DEGREE OF 

DOCTOR OF PHILOSOPHY 

JUNE 1918 



L Si^ 9 



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CONTENTS 

Page 

Introduction c 

Materials and methods 5 

Potato wilt z- 

Historical g 

Symptomology of potato wilt conditions in Minnesota 8 

Etiology of wilt of potato in Minnesota 10 

Etiology of foot rot 10 

Occurrence of Fusarium oxysporum in potato plants 10 

Artificial inoculations with F. oxysporum on potato plants 12 

Field studies with seed tubers from wilted plants 13 

Fusarium dry rot of potato tubers 14 

Historical 14 

Distribution 1 ^ 

Symptomology 1 g 

Etiology 16 

Experimental jg 

Fusarium diseases of certain truck crops 19 

Wilt and root rots of Pisum sativum 19 

Root rots of the bean (Phaseolus vulgaris) 20 

Fusarium diseases of other truck crops in Minnesota 20 

Muskmelon wilt 20 

Rots of vegetables 21 

Fusarium ear rots of corn 21 

Effect of temperature on various Fusaria 22 

Effect of moisture, light, age, food 24 

Relations to moisture 24 

Light 24 

Age 24 

Food 25 

Cross-inoculations 26 

Does the substratum alter the pathogenicity of Fusaria? 28 

The production of "toxic substances" by Fusaria 28 

"Mixed culture" relationships 31 

General discussion ^ 

Control measures 35 

Potato wilt 35 

Potato dry rot $j 

Summary 37 

Bibliography 40 

Explanation of plates 45 



STUDIES ON FUSARIUM DISEASES OF POTATOES 
AND TRUCK CROPS IN MINNESOTA 

By G. R. Bisby 

INTRODUCTION 

Fusarium wilt was reported (72) as causing a loss of more than 
twenty-five million bushels, or 4.54 per cent of the potato crop of the 
United States in 1917. Despite the large damage due to Phytophthora 
infestans in this country the same year, the total loss reported from 
Fusarium wilt was greater. Besides the injury from wilt, Fusarium 
tuber rots in the field, in storage, and during transportation may de- 
stroy from 10 to 50 per cent of the crop (37, 43, 72, 75). 

Minnesota is one of the states in which typical Fusarium wilt has 
been serious. Certain symptoms atypical of wilt have also been under 
observation for some time, particularly in the Red River Valley. The 
study of this rather anomalous disease has received particular atten- 
tion. Fusarium dry rot was also found to present, in Minnesota, 
certain phases not emphasized heretofore. The writer has also studied 
certain Fusarium diseases of other truck crops as well as those of 
the potato. 

The genus Fusarium was established by Link in 1809 (34). Var- 
ious changes in the use of generic and specific names for the fungi in 
question were made during the succeeding century; the species added 
were often imperfectly described, and the host or substratum served 
frequently as the chief distinguishing diagnostic character. Smith 
and Swingle in 1904 (63) were forced to revert to the oldest avail- 
able name to designate the Fusarium on potato, viz., F. oxyspor^m 
Schlechtendal, 1824. Appel and Wollenweber in 1910 (2) published 
a monograph of the genus Fusarium, and were able accurately to 
define several species. The literature to the year 1910 is also sum- 
marized. Wollenweber (76), Lewis (32), Sherbakoff (59), and others 
have also worked intensively on the Fusarium problem and described 
several new species. The name Fusarium oxysporum is, however, 
still applied to the fungus commonly causing wilt of potatoes. 

MATERIALS AND METHODS 

Isolations were made during the summers of 1916, 1917, and 1918 
from potato plants showing various wilt symptoms. The plants were 
obtained from sections of Minnesota north of St. Paul, particularly 



6 MINNESOTA BULLETIN 181 

the Red River Valley region. Several cultures of Fusaria isolated in 
1914 and 1915 were furnished by A. G. Tolaas. During the winters, 
isolations were also made from rotted potato tubers. Isolations were 
made from garden beans and peas, sweet corn, cucurbits, and toma- 
toes. Several hundred cultures were studied and numerous inocula- 
tions were made in the laboratory, in the greenhouse, and in the field 
in 1917 and 1918. 

Various culture media were used, particularly rice and potato 
plugs, sweet clover stems, the common agars for dilutions, and 5 and 
10 per cent dextrose agar for color reactions. The ordinary methods 
of technique were used unless otherwise stated. 

The writer wishes to express his thanks particularly to Dr. E. C. 
Stakman and Dr. E. M. Freeman, under whom the work was done, 
for suggestions and supervision. The writer is also indebted to A. G. 
Tolaas and Dr. W. A. Orton for cultures and other help, and to Dr. 
C. D. Sherbakoff for tentative corroboration of some determinations. 
The writer is particularly grateful to Dr. H. A. Edson of the United 
States Department of Agriculture who in his visits to Minnesota has 
freely given information and ideas. 

The writer has submitted cultures of the various unidentified Fu- 
saria to Dr. Sherbakoff for such taxonomic disposition as he sees fit. 

POTATO WILT 
HISTORICAL 
Smith and Swingle (63) made the first detailed study of the wilt 
of potato caused by Fusarium oxysporum. The dry rot of tubers 
discussed by them is now generally considered to be caused chiefly 
by other species of Fusarium. They described in detail the effects of 
the wilt fungus on the plant and its entrance into and spread within 
the tuber. They studied the behavior of the fungus on various media. 
Control methods for wilt were suggested. While the earlier publica- 
tion of Stewart (65) on "Another 'stem blight of potato" deals with 
a disease similar to wilt, Stewart (66) decided in 1898 that, the blight 
was not communicable and "not caused by any vegetable organism," 
and recently stated, in letters dated Nov. 18 and 30, 1918, "While 
the symptoms point to Fusarium wilt, I doubt that it was actually 
that disease." However, "If it is true that tubers showing pronounced 
discoloration of the fibro-vascular bundles, owing to the infection 
with Fusarium wilt, do not usually produce affected plants, then there 
is some reason for believing that my Long Island stem-blight was in 
reality Fusarium wilt. The tubers which were planted in my experi- 
ments were all very definitely affected by the stem-end browning. 



FUSARIUM DISEASES IN MINNESOTA 7 

Every piece planted showed the stem-end browning. Accordingly, 
it seems to me that more diseased plants should have resulted." 
Clinton's description in 1895 (11) of a "Bundle blackening of tubers" 
may have been of the ring discoloration caused by F. oxysporum. He 
wrote in a letter dated Dec. 3, 1918, "While the tubers mentioned may 
quite likely have been connected with such a wilt, I have no positive 
information that they were." 

Orton in 1909 (40) reported that the accumulation of F. oxysporum 
and other fungi in the peat soils of sections of California soon made 
the growing of potatoes unprofitable. Manns (36), as a result of his 
work, recommended clipping the stem ends of infected tubers. This 
is now a commonly used control method. Orton in 1914 (42), in 
comparing wilt due to F. oxysporum with leaf roll and other diseases, 
considered that wilt was "apparently a disease of warmer climates," 
altho he recognized that "in Minnesota wilt appears to be present in 
the older communities." 

Discussing the occurrence of this disease in Europe, Appel (1, p. 
143) states, "The [wilt] disease occurs in Germany also, but is of 
much less importance." Nicholls (38) reported the presence of F. oxy- 
sporum. in Tasmania, and Carpenter (10) found this fungus in potato 
vines and tubers in Hawaii. Reports of F. oxysporum from other 
countries are doubtful, since this name has been loosely used. 

Jones (27) found potato wilt especially in the older communities 
in Wisconsin. Milbrath (37) noted its seriousness in North Dakota, 
and its importance in Minnesota has been recognized for some time 
by Stakman and Tolaas (64). Kohler (30) may have referred to the 
stem end browning caused by F. oxysporum, tho it may be inferred 
that dry rot of tubers was also involved in the rot he attributed to 
"an undetermined species of Fusarium." 

Carpenter (8), Link (33), and others have shown that F. oxyspo- 
rum can produce a rot of potatoes. This is not in agreement with 
Wollenweber's (76) conclusion that members of the Elegans section 
of the genus Fusarium cause wilt but not rot. F. eumartii Carpenter, 
belonging to the section Martiella (76, p. 30), has been found by Has- 
kell (20) and C. R. Orton (39) to cause a stem rot and wilt of potato 
plants, as well as a rot of the tubers. "Potato wilt" may, therefore, be 
due to more than one species of Fusarium, possibly following certain 
geographical limits. Orton (42) reported the symptoms of Verticil- 
lium wilt to be similar to those of Fusarium wilt and stated that the 
distribution of the former was restricted more particularly to the 
northern states. Verticillium wilt is reported (72) to be especially 
serious in Oregon. Appel (1) has noted (referring presumably par- 
ticularly to Minnesota) symptoms atypical of the common potato wilt. 



8 MINNESOTA BULLETIN 181 

SYMPTOMOLOGY OF POTATO WILT CONDITIONS IN MINNESOTA 

The symptoms have been fully described by other writers, and 
in general agree with those found under Minnesota conditions. Coons 
(13) recently noted that in Michigan the disease may exhibit two 
aspects; one, a rapid wilting in which the vine dies when the tubers 
are about half grown; and another characterized by the dying of the 
plants "at the close of the growing season." He found these symptoms 
to depend perhaps on whether the infection is from the seed piece 
or from the soil. 

Figures 1 and 2 show the wilt symptoms common in Minnesota 
fields. Except in more severe cases, the plants do not begin to wilt 
until about blossoming time or later. The symptoms on the upper part 
of the plants are apparently those resulting from a considerable reduc- 
tion in water supply. A cross-section of the lower stem reveals the 
browning of the vascular system and often of the other tissues as well. 
This browning may extend to the tips of the plants, tho the bundles 
are often free from hyphae in these upper discolored areas. The roots 
are usually affected seriously. The tubers, which have ordinarily had 
an opportunity to develop considerably before the wilting of the plant 
stops their growth, may be affected at the stem end, as fully described 
in the literature. 

Atypical wilt symptoms such as those mentioned by Appel (1, p. 
147) have received particular attention. Other observers had noticed 
these atypical symptoms, particularly in 1914 and 1915 in the Red 
River Valley, and had considered that they might be caused by the 
blackleg organism or some species of Fusarium. For convenience the 
term "foot rot" will be used to indicate the condition in question. 
The writer found some of this disease in 1916, practically none in 1917, 
but in August, 1918, it was found in Polk and Clay counties in the 
form more characteristic of that seen by Appel, Edson, Stakman, 
Orton, and others in 1914 and 1915. 

Plants affected with foot rot are shown in Figures 3, 4, and 5. 
There is a dark brown or almost black discoloration of the lower and 
underground portions of the stem. These discolored areas are often 
rotted. When secondary organisms are present there may be a typical 
soft rot. While the symptoms resemble those of blackleg somewhat, 
there is not the inky black, slimy rot characteristic of blackleg. The 
disease is, however, confused with blackleg by growers and others. 

There is a more abundant development of hyphae in the primary 
vessels and other tissues of the stem than in stems affected with 
ordinary wilt. The effect on the roots and stolons is similar to that 
on portions of the lower stem (see Figure 5). The stem end of the 



FUSARIUM DISEASES IN MINNESOTA 9 

tuber may be attacked, and the way paved for invasion by secondary 
rotting organisms. The above-ground portions of the plant succes- 
sively wilt, die, and eventually collapse. Fortunately this foot rot oc- 
curs more particularly late in the season, as is also ordinarily the case 
with wilt in Minnesota, so that a considerable crop of tubers may 
already have been produced. These tubers are, however, liable to suf- 
fer considerable injury before or during storage from the invasion of 
Fusaria and other organisms through the injured point of attachment 
of the tubers to the affected stolons. 

The relation of this foot rot in Clay County, Minnesota, to the 
weather (United States Weather Record, Moorhead Station) during 
the 5 years this condition has been under observation is shown in 
Table I. 



TABLE I 
Relation of Weather to the Development of Foot Rot 







Precipitation 




Average temperature 




Year 










Notes on the 




















disease 




May 


June 


July 


August 


May 


June 


July 


August 






Inches 


Inches 


Inches 


Inches 


Degrees 


Degrees 


Degrees 


Degrees 




1914 


1.47 


8.92 


3.65 


2.89 


57.4 


64.8 


73.1 


65.0 


Abundant 


1915 


3.93 


9.13 


2.22 


1.05 


51.7 


59.2 


65.2 


65.2 


Present 


1916 


3.76 


4.28 


5.30 


2.87 


53.0 


60.3 


75.9 


67.2 


Present 


1917 


0.38 


1.52 


0.81 


0.77 


53.6 


61.3 


75.2 


66.4 


Absent 


1918 


2.73 


1.79 


2.68 


4.90 


55.0 


64.4 


67.7 


69.4 


Present late in 
season 


Normal 


2.95 


4.13 


3.74 


3.10 


54.8 


64.14 


68.7 


65.9 


_ j 



More than double the normal precipitation occurred in June, in 
1914 and 1915. The rainfall was especially heavy in July, 1916. The 
season of 1917 was very dry, while in 1918 it was dry until late July 
and early August, when there was considerable precipitation. Moder- 
ately high temperature is also undoubtedly a factor in producing Fusa- 
rium wilt, altho, as shown by the temperature in July, 1917, the atyp- 
ical foot rot does not occur as a result of high temperature without 
abundant rainfall; and as indicated in 1915, these symptoms may ap- 
pear in a year of high precipitation even with temperatures consid- 
erably below normal. Observations indicate further that foot rot 
attacks the plants seriously only later in the season, even tho weather 
conditions from planting time on have been favorable to its develop- 
ment. Kohler (30) described Fusarium diseases of potato in Minne- 
sota, and the foot rot condition may have been involved. He stated 
that "This disease does great havoc in wet years." Poor yields were 
obtained from planting tubers showing rot. 



10 MINNESOTA BULLETIN 181 

ETIOLOGY OF WILT OF POTATO IN MINNESOTA 
The fungi isolated from various parts of wilted plants, particularly 
the interior of the stem near the surface of the soil, from several 
regions in Minnesota, especially the Red River Valley, were predom- 
inantly Fusaria. Verticillium was obtained in only a very few cases, 
and then in association with other organisms, indicating that it was 
only saprophytically or accidentally present. There was no evidence 
that Verticillium wilt is important in Minnesota. Most frequently the 
cultures obtained were determinable as Fusarium oxysporum by the 
character of their conidia, the salmon to lilac color of the medium 
(potato or rice), the dark bluish green sclerotia, and the buff sporo- 
dochia. As was to be expected, contaminations were sometimes pres- 
ent, and other Fusaria than F. oxysporum developed occasionally. 
Sometimes the difficulty in obtaining a "high culture" (Appel and 
Wollenweber 2, p. 22) of the Fusarium rendered identification some- 
what less certain, owing to the paucity of macroconidia produced, or 
to the suppression of some other distinguishing character. The cul- 
tures were, however, run along with authentic F. oxysporum obtained 
originally from Wollenweber's laboratory (Nos. 3315 and 3394) 
through the courtesy of Dr. W. A. Orton. Specimens were also sub- 
mitted to Dr. C. D. Sherbakoff for identification. 

Ordinary wilt of potato in Minnesota appears, then, to be due, at 
least predominantly, to Fusarium oxysporum. This fungus has also 
been isolated several times from tubers showing brown ring discolora- 
tion. It was thus obtained from tubers grown as far north as Kittson 
County, in the extreme northwestern corner of the state. 

ETIOLOGY OF FOOT ROT 
Isolations were made from numerous wilted plants showing atyp- 
ical wilt symptoms in the expectation that organisms other than F. oxy- 
sporum were the causal agents. Some isolations obtained by A. G. 
Tolaas from atypically affected plants in 1914 and 1915 were identified 
by the writer. The fungus obtained from plants showing foot rot 
symptoms was found in the majority of cases to be F. oxysporum and, 
as already indicated, the unusual appearance is attributed particularly 
to the heavier precipitation resulting in a watersoaked condition of the 
soil. This is most likely to occur in a heavy soil such as that in the 
Red River Valley. Other fungi and several bacteria were also isolated, 
but all the evidence indicated that they were merely saprophytes. 

OCCURRENCE OF FUSARIUM OXYSPORUM IN POTATO PLANTS 
In the course of development of the wilt or foot rot disease, con- 
siderable amounts of the infecting fungus are of course accumulated 
in the tissues of the potato stems, roots, stolons, and even in the tubers. 



FUSARIUM DISEASES IN MINNESOTA n 

The following observations indicate that the fungus may grow on 
other parts of the plant also, and develop in greater abundance on 
those parts mentioned. 

On vines affected with wilt in the field and placed two or more 
days in a moist place, a luxuriant growth of fungus may develop. 
(See Figure 4.) From the surface and the interior of these vines, 
F. oxysporum was isolated. Not infrequently the mycelium and spores 
of F. oxysporum may have developed abundantly in the somewhat 
hollow areas within the stem of plants affected in the held. Plants 
affected with wilt or foot rot may thus cause heavy contamination 
of the soil. 

Isolations were made on September 10, 1917, to determine if F. 
oxysporum might be present more or less saprophytically in the stems 
of plants late in the season. This was shortly after a frost had prac- 
tically destroyed the leaves. These plants had been grown at Univer- 
sity Farm, part of them from northern grown seed, had not shown 
signs of wilt, and had produced a good crop of healthy tubers. Below 
the surface of the soil the inside of these stems was browned, and 
from some such stems "high cultures" of F. oxysporum were readily 
obtained. Similar isolations were made later in 1917, and several on 
October 1 and 2, 1918. The isolations made in 1918 were from the 
old stems of normal plants which had been killed by frost. They were 
taken from a field in Hennepin County which had been sprayed 
with bordeaux mixture, and which had yielded 214 bushels per acre. 
F. oxysporum was obtained consistently from this material. 

The "dry stem rot" of potatoes with which Rhizoctonia is asso- 
ciated is common in Minnesota. That Fusarium oxysporum may occa- 
sionally be a factor in causing this condition is indicated by the fact 
that it was isolated from the external stem lesions of plants affected 
with "stem rot," as well as from the interior of such stems. The 
interior of potato stems affected with dry stem rot is often browned, 
especially near the base. Edson and Shapovalov (15) have shown 
recently that various fungi, including F. oxysporum, may cause stem 
lesions. Rhizoctonia hyphae may of course be present even if they 
are not the primary cause of the lesions. 

The seed piece under the growing plant is often rotted. If the rot 
is caused by bacteria it is soft and foul smelling. Species of Fusarium 
may cause a dry rot. The rot of the seed piece may be soft and 
without a foul odor. Isolations were made in the season of 1917 
from several such cases as the last two. The specimens were obtained 
from University Farm and other parts of the state. F. oxysporum 
was often obtained from seed tubers affected with soft rot. From 
tubers affected with dry rot, F. discolor sulphureum (Schl.) App. 



12 MINNESOTA BULLETIN 181 

and Wr. and other Fusaria were obtained. Bacteria and other fungi 
were of course commonly present as secondary organisms. No diffi- 
culty was experienced in securing a more or less soft rot of potato 
tubers with F. oxysporum by artificial inoculation. 

Considerable mycelium of F. oxysporum may occur in and on the 
leaves of plants growing under moist conditions, even when the lower 
stem does not show the presence of the fungus. Such leaf infection 
may presumably result from inoculum carried by insects or spattered 
by rain. Milbrath (37) reports that leaves may be affected, altho he 
may have meant only internally. (See also 15.) Cases of external as 
well as internal infection of leaves and petioles have been secured 
from artificial infection in the greenhouse. 

The relation of F. oxysporum to the soil is discussed in another 
section. • 

ARTIFICIAL INOCULATIONS WITH F. OXYSPORUM ON POTATO 

PLANTS 

Many preliminary experiments in the greenhouse and in the field 
to secure infection and wilt of potato plants by artificially inoculating 
F. oxysporum into the seed piece planted, or into the soil, were unsuc- 
cessful. An examination of the literature indicates also that other 
workers have not had great success in securing infection of potato 
plants with the wilt organism under ordinary conditions. It is evident 
that F. oxysporum is not vigorously parasitic to actively growing potato 
plants. 

Sometimes such results as shown in Figure 6 were obtaineH under 
greenhouse conditions. Rotting of the seed piece, browning of the 
stem, and death of the leaves ensued from inoculating the seed tuber 
with F. oxysporum. This is hardly characteristic of Fusarium wilt, 
however, tho resembling the foot rot condition. 

In view of the possibility that the average temperature in the 
greenhouse during the winter months was not sufficiently high for 
good infection, the cage shown in Figure 7 was constructed, and 
heated with two carbon electric light bulbs. A soil temperature of 
from 20 to 30 degrees could thus be maintained. The humidity was 
of course also high. Figures 8 and 9 show a type of injury resulting 
from inoculating sterilized soil heavily with F. oxysporum under these 
warm and damp conditions. This injury was caused several times 
with F. oxysporum, and F. radicicola Wollenw. caused a similar injury 
in one trial. Fitch and Bennett (17) illustrate a somewhat similar 
condition as found in the field. Link (33) also secured stem rots in 
the laboratory with F. oxysporum. Injuries such as are illustrated 



FUSARIUM DISEASES IN MINNESOTA 13 

in Figures 8 and 9 are considered entirely comparable with the natur- 
ally occurring foot rot condition illustrated in Figures 3 and 4. 

Figures 10 and 11 show two infected plants resulting from a lighter 
infection of the soil, and are believed to represent a fair greenhouse 
manifestation of Fusarium wilt. It is to be noted that the upper 
leaves show the characteristic rolling (see 1, p. 143). The higher 
temperatures in the warm chamber, while allowing infection, were un- 
favorable to the potato. Plants placed inside the chamber died sooner 
than corresponding plants left outside. 

FIELD STUDIES WITH SEED TUBERS FROM WILTED PLANTS 
Wilted plants do not result from planting infected seed, unless 
conditions are favorable to the development of the fungus. These 
conditions, particularly a high temperature, are often at the same 
time unfavorable to the potato. Seed from vines wilted in the field, 
showing more or less of the bundle blackening, usually produced plants 
in the greenhouse similar to those from normal seed. Such seed 
planted in the field in 1917 in not seriously infected soil gave no more 
wilt than several plots from ordinary seed. 

A fairly extensive study of the effect of planting tubers produced 
under wilted vines was made in the field in 1918. Late in the summer 
of 1917 several Green Mountain potatoes were dug by hand from 
under badly wilted vines in Clay County, Minnesota. There was no 
marked amount of stem end discoloration of the tubers at digging 
time, nor did this vascular browning increase appreciably through the 
winter. Through the courtesy of Dr. G. H. Coons, a half bushel of 
tubers was obtained in the spring of 1918 from a field in Michigan 
which had shown from 30 to 40 per cent of wilt. Plantings were 
made in the field at University Farm. The tubers from Clay County 
were planted whole, and those from Michigan were divided into two 
lots. Several isolations were made from one lot to determine the 
fungi present in the browned vascular tissue of the stem end of the 
tubers. F. oxysporum and various other Fusaria were obtained. The 
other lot was used for planting, and the tubers were sorted into two 
groups according to size. The smaller tubers were halved to give eye 
and stem ends, and the larger tubers were cut longitudinally through 
the former point of attachment of the stolon, then cut transversely, 
to give two each of approximately equal eye ends and stem ends. 
These were planted in two places on University Farm. The stand of 
the potatoes obtained from Michigan was poor, owing particularly 
to frost necrosis of the tubers (29) and to the fact that the "seed" 
had been obtained from seriously affected plants. It was also neces- 
sary to plant the tubers rather late in the spring. The seed pieces were 
planted \6y 2 inches apart in rows 3 feet apart. 



14 



MINNESOTA BULLETIN 181 



The average yield of the tubers from Clay County was slightly 
more than one pound per hill (29y 2 pounds from 25 hills) or at the 
rate of 180 bushels per acre. The plants were not wilted. The yield 
indicates that the seed was not affected ; indeed, it is possible that the 
greater immaturity of such seed resulted in added vigor of the progeny. 

The results with the seed from Michigan are summarized in 
Table II. 





TABLE II 
Result of Planting Tubers From Badly 


Wilted Vines 




Character of 
seed piece 


Date 
planted 


Area of 
plot* 


No. of wilted 
plants 


Yield 


Rate per 
acre 


Eye quarters 
Stem quarters 
Eye halves 
Stem halves 


June 4 
June 4 
June 4 
June 4 


Sq. Ft. 
268.5 
268.5 
148.5 
148.5 



2 
2 
1 


Pounds 
32.0 
23.0 
12.0 
14.5 


Bushels 
86.5 
62.2 
58.4 
70.9 



* Including proper marginal area abou„ plot. 

In 1918 a plot of the eight standard varieties (6) was planted, 
and a considerable amount of fungus from cultures of F. oxysporum 
introduced into the soil beside each seed piece at planting time. Here 
again only healthy plants were produced, indicating that none of the 
varieties is particularly susceptible to the fungus, unless other factors 
are conducive to the development of wilt. 

The data presented in Table II indicate that serious disease does 
not necessarily follow from planting seed from wilted vines, and that 
no more wilt may result from the use of the stem ends than from 
the use of eye ends. Other observations support this view. Wilted 
plants do not, of course, produce tubers of as good quality as healthy 
plants, and it can not be denied that infected tubers may introduce 
more of the disease into the soil. Such seed is considerably less desir- 
able than seed from healthy plants, and plants affected with wilt 
should be rogued from plots to be dug for seed. Selecting seed or 
clipping the stem ends is, however, not alone sufficient to avoid loss 
from wilt. The considerations involved in the use of affected seed 
from the north for planting in the southern states require further 
attention. 



FUSARIUM DRY ROT OF POTATO TUBERS 
HISTORICAL 
Some of the earlier literature regarding Fusarium rots of potato, 
both American and European, is summarized by Smith and Swingle 
(63) and in part by Manns (36), altho these authors did not distin- 
guish between the Fusaria causing dry rot and those causing wilt. 



FUSARIUM DISEASES IN MINNESOTA 15 

The monograph by Appel and Wollenweber (2) made it possible to 
distinguish between species of Fusaria. Jamieson and Wollenweber 
(25) reported F. coeruleum (Lib.) Sacc. and F. discolor sulphureum 
to occur in Germany as wound parasites, and the American F. tricho- 
thecioides Wollenw. was described and reported from Washington, 
Minnesota, Iowa, Nebraska, and South Dakota. Inoculation studies 
were described. F. tuberivorum Wilcox and Link (75) was consid- 
ered a synonym of the previously established F. trichothecioides. 
Orton (41) in 1913 gave a brief description of this "powdery dry 
rot" and suggested methods of control. Wollenweber (76) distin- 
guished sharply between wilt- and rot-producing Fusaria. Carpenter 
(8), besides showing that this sharp distinction did not hold for tuber 
rots, described F. eumartii as a new species of Fusarium causing dry 
and wet rot of tubers. He also reported F. radicicola as producing 
tuber rot through wound infection. Pratt (49, 51, 52) showed that 
F. radicicola and F. trichothecioides were apparently well distributed 
through the western desert soils, and suggested disinfecting the stock 
before storage or the use of cold storage, as a control measure against 
rot. Link (33) has shown that F. trichothecioides can cause wilt as 
well as rot, and also that F. oxysporum can cause rot as well as wilt. 
Sherbakoff (59) stated that the Fusarium most commonly producing 
potato rot in the eastern United States is F. coeruleum. Pethybridge 
(46, 47, 48), in Ireland, performed experiments with dry rot of pota- 
toes which he considered due to F. coeruleum. Orton (39) and Has- 
kell (20) have found that F. eumartii can cause, besides a tuber rot, 
a wilt or stem rot of the potato plant. Milbrath (37) reported dry 
rot to be serious in North Dakota, causing a loss of "over 20 per cent 
in all storehouses in the Northwest" in 1914. Altho he did not specify 
which Fusarium was responsible, it is noteworthy that Cai-penter 
mentions having isolated F. discolor sulphureum from tubers sent in 
by Milbrath, as well as from tubers obtained from South Dakota. 
Other references to F. discolor sulphureum (2, 25, 59, 76) mention 
its presence in Germany, and nowhere has the writer seen it referred 
to as being serious in the United States. 

DISTRIBUTION 
In the United States, Fusarium dry rots appear to be widely dis- 
tributed east and west, but the north central part of the country has 
not been very critically surveyed. In Minnesota, isolations have been 
made from tubers grown in Kittson, Pennington, Polk, Norman, Mah- 
nomen, Clay, Wilkin, Otter Tail, Bigstone, Swift, and Lincoln coun- 
ties, along the western side of Minnesota, and from Brookings County, 



16 MINNESOTA BULLETIN 181 

South Dakota. Some have also been made from the region of the 
Twin Cities and from Crow Wing and Kanabec counties. 

SYMPTOMOLOGY 

The Fusarium dry rot of potatoes found in Minnesota is a brown, 
compact, firm rot, without the foul odor of bacterial rots. Cavities 
are often present in the tissues. These cavities and the tissues con- 
tain considerable mycelium which develops readily and abundantly 
when the tuber is placed in a damp chamber. From the edges of the 
rotted areas, pure cultures of the fungus may usually be obtained 
directly from tissue cultures. The skin of the potato is often wrin- 
kled. Figures 12, 13, and 14 show the appearance of this rot as found 
in storage. The rot starts at any point on the potato, and in the case 
of stored potatoes usually from a wound. It is more abundant as the 
winter advances. It does not have the powdery appearance charac- 
teristic of the rot caused by F. trichothecioides, because the spore 
masses when present are more compact and less dry. 

Sections of rotted potato show that the fungus grows through 
the cells in considerable abundance. The observation of Orton (39) 
and Pratt (49) that a dry rot fungus has a tendency to follow the 
vascular system can be confirmed in tubers rotted by F. discolor sul- 
phureum. The writer's experience in general corroborates Carpenter's 
observations (8) that there is no real distinction between the effects 
of Fusaria causing dry and soft rots, altho F. discolor sulphureum 
under ordinary conditions produces a dry rot. 

ETIOLOGY 
F. discolor sulphureum was obtained readily from affected tubers 
grown in many parts of Minnesota. Altho the fact that this Fusarium 
is the cause of a dry rot of potatoes has not been emphasized, it is 
one of the most common causes of rot in Minnesota, particularly in the 
Red River Valley. The ability of this fungus to cause dry rot has 
been demonstrated frequently. 

EXPERIMENTAL 

Efforts to determine varietal differences in susceptibility were un- 
successful. The eight standard varieties for Minnesota (Brown and 
Wellington, 6) were used, and rot developed from wound inoculations 
in each variety. 

A series of experiments was made to determine the relations of in- 
jury to the tuber and of moisture and temperature to the development 
of the rot caused by F. discolor sulphureum. Tubers were inoculated 
on the uninjured epidermis, on the surface after slight wounding with 



FUSARIUM DISEASES IN MINNESOTA 



17 



a sterile scalpel, and in deeper cuts into the tuber. Sets of inoculated 
tubers were kept at different temperatures under damp conditions, 
and similar sets in dessicators containing calcium chloride. The re- 
sults are summarized in Table III. (See Figure 15.) The extent and 
rapidity of the rot is proportional to the seriousness of the injury to 
the tuber, tho the fungus may sometimes enter through uninjured 
surfaces, probably through lenticels. The later series of inoculations 
(December, 1918), incubated for 13 days (see Table III), resulted in 
less infection than in the previous experiments. A less vigorous 
"strain" of the Fusarium may have been used. There are character- 
istic differences in the rot developed at different temperatures. Under 
cooler conditions, the tissues are darkened and contain few "pockets" 
and few spores. It is evident that the fungus can rot tubers readily 
under dry conditions, especially if it gains entrance through wounds. 
The absence of wounds appears to retard the development of F. dis- 
color sulphureum more than dryness or storage temperature, except 
in the case of cold storage. 



TABLE III 

Effect of Injury, Temperature.^^ Moisture Upon~the Occurrence of the Rot of 

Potatoes Caused by F. discolor sulphureum 



Character of 






Tubers 






injury 


Moisture 


Temperature 


inoculated 


Time 


Results 






Degrees 




Days 




None 


Saturated 


1.1-1.7 


4 


30 


No rot 




Saturated 


8-10 


4 


12 


No rot 




Saturated 


8-10 


9 


13 


No rot 




Dessicator 


8-10 


4 


12 


Slight rot in some cases 




Dessicator 


8-10 


8 


13 


No rot 




Saturated 


Room 


4 


12 


Slight rot in some cases 




Saturated 


Room 


8 


13 


No rot 




Dessicator 


Room 


6 


12 


Slight rot in some cases 




Room humidity 


Room 


4 


12 


Slight rot in some cases 




Saturated 


25 


6 


13 


No rot 




Dessicator 


25 


6 


13 


No rot 


Slight 


Saturated 


1.1-1.7 


4 


30 


Trace rot 




Saturated 


8-10 


4 


12 


Moderate rot on all 




Saturated 


8-10 


9 


13 


Slight rot on 3 tubers 




Dessicator 


8-10 


4 


12 


Moderate rot on all 




Dessicator 


8-10 


8 


13 


Slight rot on 4 tubers 




Dessicator 


Room 


6 


12 


Moderate rot on 4 tubers 




Saturated 


Room 


4 


12 


Moderate rot on all 




Saturated 


Room 


8 


13 


Slight rot on 2 tubers 




Saturated 


25 


6 


13 


Slight rot on 2 tubers 




Dessicator 


25 


6 


13 


Slight rot on 3 tubers 


Considerable 


Saturated 


1.1-1.7 


8 


30 


Slight rot 




Saturated 


8-10 


6 


12 


Much rot. on all 




Dessicator 


8-10 


6 


12 


Moderate rot on all 




Dessicator 


Room 


4 


12 


Much rot on all 




Saturated 


Room 


4 


12 


Much rot on all 




Room humidity 


Room 


4 


12 


Much rot on all 




Saturated 


25 


5 


12 


Much rot 



18 MINNESOTA BULLETIN 181 

Pethybridge (47) has reported that young sprouts of uninjured 
tubers may be killed by heavy inoculations with F. coeruleum. F. dis- 
color sulphureum likewise injures young sprouts if present in 
abundance. 

Sherbakoff (59) and Pethybridge (47) have found that potato 
tubers rot more readily after sprouting. To determine the relative 
susceptibility to rot of old and new potatoes, several inoculations were 
made October 16, 1917, on recently harvested tubers and on tubers 
of the 1916 crop kept in cold storage for more than a year. The latter 
had sprouts only about fifteen millimeters long at the beginning of the 
experiment. At room temperature under a bell jar, the tubers grown 
in 1916 showed, October 26, about twice as large an area of rot as did 
those of the 1917 crop. The difference was due partly to greater 
shrinkage of tissue in the older potatoes. Nevertheless the newer 
potatoes had developed a considerable amount of rot. Additional 
tests with sprouted and non- sprouted tubers grown the same year 
indicated that while sprouted tubers usually rotted more extensively, 
sprouting was not at all a controlling factor in the development of the 
rot. In sprouted tubers there is a marked shrinkage of the tissue. 
Naturally infected tubers frequently rotted before the appearance of 
any sprouts. 

Experiments to determine the effect of the fungus on tubers show- 
ing frost necrosis (Jones and Bailey, 29) as compared with healthy 
tubers, were made by inoculating, at the same time, both kinds of 
tubers. These experiments failed to show that the injury by frost had 
increased susceptibility to rot. Likewise, it was found that the tubers 
from "constitutionally degenerate" plants which had shown the so- 
called curly dwarf symptoms were no more susceptible to the rot 
caused by F. discolor sulphureum than were normal tubers. Indeed, 
the degenerate tubers often showed smaller rotted areas than did the 
healthy tubers. 

No characteristic wilting of the foliage resulted on potato plants 
grown from tubers infected with F. discolor sulphureum. Several 
trials for the purpose of determining the effect of planting diseased 
tubers under field and greenhouse conditions gave the following results : 

1. If the tuber or seed piece were badly affected at planting 
time, the continued rotting frequently resulted in the destruction of 
the sprout. Sometimes this destruction of the seed piece and the sprout 
ensued even when only a small amount of rot was present at planting 
time. 

2. If the sprout were well started before the seed piece was com- 
pletely rotted, it usually continued to grow, altho the resulting plant 
was unthrifty, owing to the loss of the reserve food in the seed piece, 



FUSARIUM DISEASES IN MINNESOTA 19 

and also perhaps in part to the presence of "toxic substances" (see 
below) in the rotting tissue in contact with the base of the sprout. 

3. The rot might not develop rapidly enough to affect the sprout 
or growing plant. (Figures 16, 17, and 18 show examples of cases 
2 and 3.) 

Fusarium trichothecioides Wollenw. has been reported from St. 
Paul (25, 8). The writer is uncertain as to whether the tubers referred 
to were grown in St. Paul or collected there. At any rate, he has 
never isolated F. trichothecioides from a potato grown in Minnesota. 
This, of course, does not mean that it does not occur, since the whole 
state has not as yet been thoroly surveyed for tuber rots, but this 
Fusarium is apparently not abundant. It has been isolated several 
times from potatoes shipped in from western points, including one 
lot from North Dakota. 

FUSARIUM DISEASES OF CERTAIN TRUCK CROPS 

Fusarium injuries may be of considerable importance to various 
truck crops in the United States (71), even tho a definite wilt is not 
produced. Root rots and stem injuries due to Fusaria are rather com- 
mon on several crops. Members of the Leguminosae (see 60) such 
as cowpea, pigeon pea, and soybean, are seriously affected. 

WILT AND ROOT ROTS OF PISUM SATIVUM 
* Fusarium vasinfectum pisi was established by Van Hall (73) as 
the cause of St. John's disease of the garden pea. The Fusarium 
which Schikorra (60) assigned to the same species was determined 
by Appel and Wollenweber (2) to be identical with their species F. fal- 
catum, which was reported to occur on garden peas in Germany, and 
on tomato fruit in Germany and the United States (76, 59). Lewis 
(32) isolated a Fusarium from diseased Pisum sativum in Maine, 
which Wollenweber determined as F. or t hoc eras App. and Wr. Wol- 
lenweber (76) also described a new species, F. redolens, with the 
following notes: "Vascular parasite, cause of wilt and foot disease 
of Pisum sativum. Distribution unknown." This author also con- 
sidered that "More than one species, differing both in size of conidia 
and color of conidial masses, may cause the St. John's disease of the 
garden pea." 

Little information is as yet at hand regarding the distribution or 
seriousness of Fusaria affecting the garden pea in the United States. 

The first report of a serious outbreak of this disease in Minnesota 
came in late June, 1916, from Le Sueur. The disease caused con- 
siderable damage in a field of about 16 acres. A wilt of garden peas 
was reported from near Kasson in 1917. 



20 MINNESOTA BULLETIN 181 

Species of Fusarium have been found (4) associated with the 
diseased condition of roots and stems of the garden pea in Minnesota. 
One species, evidently belonging taxonomically in the section Martiella 
Wollenw. (76) has been found to be particularly pathogenic. The 
stem and root injuries resulting in wilt of the pea plants have been 
obtained from infecting the soil or sterilized seeds when planted in 
either sterilized or unsterilized soil. If considerable inoculum be ap- 
plied, the seeds may rot before sprouting or shortly after (Figure 19). 
With a less heavy infection the plants may grow to a considerable size 
before the general rotting of the roots and lower stem results in 
wilting and death. 

Studies of this disease are being made by Dr. F. R. Jones, of the 
United States Department of Agriculture, with whom the writer is 
cooperating. Cultures of the Fusarium have been submitted to Dr. 
Sherbakoff for taxonomic consideration. The writer has used this 
Fusarium in some comparative studies with other Fusaria, as reported 
later in this paper. 

ROOT ROTS OF THE BEAN (PHASEOLUS VULGARIS) 
Burkholder (7) reported Fusarium root rots of the bean to be 
serious in New York State. Reddick (55) reported that Burkholder 
found the fungus to be similar morphologically to F. martii, but differ- 
ent physiologically ; he called the fungus Fusarium martii phaseoli, and 
described experiments indicating important relations between temper- 
ature and the development of bean plants and the "hemi parasite." 
Several pathologists have reported (71, p. 8) troubles from root rots 
due probably to Fusarium, from various sections of the United States. 
Rots of the roots and lower stem of bean plants have been noted 
in Minnesota, particularly in the spring while the plants are still small 
and the ground cool. From such injured roots a Fusarium was iso- 
lated. Inoculation experiments demonstrated the pathogenicity of this 
fungus to bean plants. This Fusarium has been utilized in some tem- 
perature studies, as noted under a subsequent heading. Upon sub- 
mission of the fungus to Dr. Burkholder, he pronounced it to be prob- 
ably different from his F. martii phaseoli. 

FUSARIUM DISEASES OF OTHER TRUCK CROPS IN MINNESOTA 
Muskmelon wilt. — A Fusarium was isolated by G. R. Hoerner, of 
the Section of Plant Pathology, in 1916, from wilted muskmelon vines. 
The fungus has not been found to agree with either F. niveum E. F. 
Smith or F. vasinfectum Atk. (see 61, 71, 72). Inoculation experi- 
ments did not demonstrate that it was particularly parasitic to musk- 
melons or cucumbers. In 1918, two reports of non-bacterial wilt were 



FUSARIUM DISEASES IN MINNESOTA 21 

received from the region of the Twin Cities, and from one field Fu- 
saria somewhat similar to the one isolated in 1916 were obtained. 
The trouble did not become serious in the field in 1918, and the writer 
considers the Fusaria to have been present semi-parasitically, gaining 
entrance when the plants were in a nonvigorous condition. 

Rots of vegetables. — Fusaria causing rots of cucumber fruits have 
been isolated, and are not uncommon, affecting either green or ripe 
cucumbers. In view of the inoculation experiments reported later, 
the writer regards these Fusaria as acting semi-parasitically, not as 
specific parasites restricted to the cucumber. Lewis (32) obtained 
rots of cucumber fruits with several different Fusaria. 

Wollenweber (76) has described Fusarium sclerotium as causing 
a rot of tomato fruits, and has found that F. falcatum also causes a rot 
of tomatoes. He named a fungus obtained by Lewis (32) from tomato 
fruits, F. citrinum. The writer also has isolated Fusaria from the 
tomato fruit. A wilt of tomato such as is caused by F. lycopersici 
Sacc. in the south and F. oxysporum and F. orthoceras App. and Wr. 
in the west (24) has not been definitely found in Minnesota. 

Rots of carrot and other vegetables due to various Fusaria are 
quite common, particularly in storage and following wounds. The 
rots may be soft or dry. No specificity appears to exist between these 
fungi causing various fruit and vegetable rots and the hosts on which 
they may be found. This is also indicated by the inoculation experi- 
ments recorded later. 

Fusarium ear rots of corn (Zea mays). — Pammel, King, and Seal 
(44) have summarized the literature of Fusarium diseases of corn. 
They found that roots, stalks, and ears were attacked, but the Fusaria 
isolated were not named. Sheldon (58) described Fusarium monili- 
forme as the cause of moldy corn. Hoffer and Holbert (22) have 
recently called attention to injury to corn plants by Fusaria and 
bacteria. 

The symptoms considered by the writer have been particularly 
rots of the ear and cob, ordinarily pinkish or reddish in color. Such 
rots were widely distributed in Minnesota in 1917. As a result of 
early frosts that year, much immature corn was gathered. 

Fusaria were isolated from field corn in the crib, but more par- 
ticularly from sweet corn in the field. While inoculations have not 
been made to determine the pathogenicity, it was soon suggested from 
laboratory studies in 1917 that the Fusarium from some isolations from 
corn (both sweet and field varieties) were identical morphologically 
with F. culmorum (W. Sm.) Sacc, the wheat scab organism. Hoffer 
has been working upon this problem, and with others has published 
(23) results of cross-inoculations. 



22 MINNESOTA BULLETIN 181 

EFFECT OF TEMPERATURE ON VARIOUS FUSARIA 

The relations of temperatures affecting the development of host 
and parasite are highly important. Considering Fusaria, the work of 
Humphrey (24), Link (33), Tisdale (69), Gilman (18), and others 
is summarized by Jones (28). The papers of Reddick (55) and of 
Wollenweber (76) also deal with this question. 

Several of these authors have emphasized the fact that infection 
by the Fusarium is more serious at, or even dependent upon, a tem- 
perature near the optimum for the fungus; in the case of flax wilt, 
there appears to be a definite temperature below which the plant is not 
affected (Tisdale, I.e.). The suggestion of Reddick (I.e.) that the 
fungus may develop upon the host when unfavorable temperature has 
lowered its vitality, is important and has perhaps been partially over- 
looked. 

Several experiments were begun in 1917 to test the relation of 
certain Fusaria to temperature. While the relation of the host plants 
to the different temperatures was not critically determined, considerable 
is already known in a general way. 

The low temperature used in the experiment (1.1 to 1.7 degrees 
C.) was practically constant. The temperatures of 25, 30, and 35 
degrees were fairly constant. The medium used of course strongly 
affects the rate of growth of the fungus. In these experiments, potato 
dextrose agar was employed, and since the four Fusaria were sub- 
jected in each case to the same conditions, the data are comparable 
at each of the different temperatures. More than one set of cultures 
was run at most temperatures, and from three to eight measurements 
were made at different periods of time. A partial series run later 
and not included in the table gave figures somewhat different, tho 
a similar relation existed between the rates of growth of the four 
Fusaria at each of the temperatures utilized. 

Analysis of Table IV shows that the Fusarium from the bean can 
make a good growth at 1.1 to 1.7 degrees C, and at temperatures of 
20 degrees and below grows somewhat more rapidly than does the 
Fusarium from pea, while at 25 degrees and above the reverse is true. 
The growth of each Fusarium is comparatively more favorable at the 
temperature more unfavorable for its host. This supplements Red- 
dick's (55) observations. F. oxysporum grows well at temperatures 
unfavorable for the potato plant. F. discolor sulphur eum makes but 
slight growth at 1.1 to 1.7 degrees, but is able to cause a slight amount 
of rot at this temperature (see Figure 20). At 8 to 10 degrees, this 
fungus rots tubers readily as shown in Figure 21. 



FUSARIUM DISEASES IN MINNESOTA 



23 



TABLE IV 
The Effect of Temperature on the Rate and Character of Growth of Fusaria 







Av. daily 


No. days 


Character of 


Macroconidia or 


Temperature 


Fusarium 


growth 
in radius 


measured 


mycelium 


sporodochia 


Degrees, C. 




mm. 








1.1-1.7 


From bean 


1.4 


14 


Loose aerial 


No sporodochia 




From pea 

F. oxysporum 


None 
None 


14 
14 














F. discolor sul- 












phureum 
From bean 


Trace 
2.4 


14 
13 to 20 






8-10 


Loose aerial 


No sporodochia 




From pea 


2.0 


13 to 20 


Close to med. 


Few macroconidia 




F. oxysporum 


1.7 


13 to 20 


Thickset aerial 


No sporodochia 




F. discolor sul- 












phureum 


3.4 


13 to 20 


Loose aerial 


No sporodochia 


14-16 


From bean 


4.5 


6 to 13 


Loose aerial 


No sporodochia 




From pea 


4.2 


6 to 13 


Close to med. 


No sporodochia 




F. oxysporum 


4.5 


6 to 13 


Loose aerial 


No sporodochia 




F. discolor sul- 












phureum 


6 6 


6 to 13 


Loose aerial 


Some macroconidia 


Room temper- 


From bean 


6.6 


4 to 6 


Loose aerial 


No sporodochia 


ature 


From pea 


9.0 


4 to 6 


Close to med. 


Few sporodochia 




F. oxysporum 


12.0 


4 to 6 


Loose aerial 


Few macroconidia 




F. discolor sul- 












phureum 


13.0 


4 to 7 


Close to med. 


Many sporodochia 


25 


From bean 


6.6 


4 to 6 


Loose aerial 


Some sporodochia 




From pea 


9.0 


4 to 6 


Rather loose 


Some sporodochia 




F. oxysporum 


12.0 


4 to 6 


Loose aerial 


Few sporodochia 




F. discolor sul- 












phureum 


13.0 


4 to 6 


Close to med. 


Pseudopionnotes 


30-31 


From bean 


4.7 


4 to 6 


Loose aerial 


No sporodochia 




From pea 


9.5 


4 to 6 


Rather loose 


No sporodochia 




F. oxysporum 


9.6 


4 to 6 


Rather close 


Few macroconidia 




F. discolor sul- 












phureum 


6.0 


4 to 6 


Very close 


Abundant pseudo- 
pionnotes 


35-36 


From bean 


Trace 


8 






From pea 


4.3 


8 


Loose 


No sporodochia 




F. oxysporum 


3.2 


8 


Close to med. 


No sporodochia 




F. discolor sul- 












phureum 


Trace 


8 













From about 8 to 15 degrees C, F. discolor sulphureum develops 
a loose vegetative mass of mycelium without sporodochia, whereas at 
about 20 degrees and above macroconidia are produced, more abun- 
dantly as the temperature rises, until at 30 degrees a dense pseudo- 
pionnotes is produced, with mycelium close to or sunken in the agar. 
Removal of cultures of this fungus from higher or lower temperatures 
to room temperature allows again the development of the growth char- 
acteristic in the new temperature. (Figures 22 and 27.) The abundant 
spore production of this fungus at higher temperatures has a bearing 



24 MINNESOTA BULLETIN 181 

on the accumulation of inoculum in storage houses, and perhaps fields, 
during the summer months. 

Freezing would hardly be expected to injure Fusaria. Bartram 
(3) reported, however, that a Fusarium obtained from conifers suc- 
cumbed to temperatures occurring in winter at Burlington, Vermont. 
Cultures of F. oxysporum exposed to the outside temperature from 
December 21, 1917, to February 11, 1918, began growing again when 
brought indoors, and transfers developed normally. This exposure not 
only involved at times temperatures far below freezing, but, since the 
cultures were placed on the south side of the building, exposure to 
the sun and to alternate freezing and thawing. 

Similarly, cultures of F. discolor sulphureum were uninjured after 
exposure out of doors for more than a month during the winter. 
Wilcox, Link, and Pool (75) found that freezing did not injure F. 
irichothecioides. The frequent observation that Fusaria, and various 
other fungi as well, can overwinter in the soil shows quite clearly 
that low temperatures exert no serious deleterious effect upon them. 

EFFECT OF MOISTURE, LIGHT, AGE, FOOD 

Relations to moisture. — Fusaria grow readily in culture both on 
rather dry substances such as clover stems, and when submerged in 
liquid media. Possible oxygen relations involved have not been 
tested by the writer. That these fungi withstand dry conditions well 
is indicated by the fact that more than a year after inoculation test 
tube agar cultures of F. oxysporum were still viable ; F. trichothecioides 
was still viable after 25 months. The tubes were exposed all this 
time to the dry and often warm conditions of the laboratory. 
Humphrey (24, p. 15) reports viability of cultures containing chlamy- 
dospores after two years' laboratory dessication in a test tube. 

Light. — Cultures grow almost equally well in light or dark, altho, 
as frequently observed, the colors produced are much more vivid in 
rather bright light ; sunlight on the other hand, is unfavorable. 

Age. — That cultures of Fusaria may lose their virulence after 
some period of time on culture media is suggested as a possibility by 
Sherbakoff (59) and Link (33). The writer has not found that this 
necessarily holds true. Cultures of F. oxysporum obtained as men- 
tioned from Wollenweber's laboratory on February 8, 1915, and which 
had of course been isolated some time previously, were still able to 
cause infection of potato stems and rot of tubers about three years 
later. Appel and Wollenweber (2) note that cultures were still viru- 
lent after two years; Edson and Shapovalov (15) found that age did 
not lessen pathogenicity. It is of course true that cultures may cease 
to be "high cultures" and produce fewer macroconidia if transferred, 



FUSARIUM DISEASES IN MINNESOTA 25 

for example, only at long periods. While such cultures may not be 
as actively virulent as "high cultures," a ready way sometimes to bring 
about a high culture is by inoculation into the proper host and by 
subsequent reisolation. 

Food. — While the writer has not endeavored to determine specifi- 
cally which enzymes are produced by certain species of Fusarium, he 
has grown these fungi on various media, both synthetic and complex ; 
it is obvious that they are not restricted in their saprophytic develop- 
ment as to the food used. The work of Hawkins (21) showed that 
sucrase, maltase, xylanase, and diastase were secreted by both F. oxy- 
sporum and F. radicicola. He found these two fungi to have prac- 
tically the same effect on the potato. 

The situation with regard to the use of starch by various Fusaria 
requires special consideration. Smith and Swingle (63) noted that 
the starch grains in a rotted potato (causative Fusarium not certainly 
F. oxysporum) were not corroded, altho they found some change as 
evidenced by the staining reaction with iodine. Hawkins (I.e.) ob- 
served that starch was not used by the Fusaria with which he worked 
unless first gelatinized. Hawkins sought an explanation in the slow- 
ness of action or diffusibility of the enzyme. It may be noted, how- 
ever, that many writers consider the outer layer of the starch grain 
to be not homogeneous with the interior. Shapovalov (56) translates 
Naumov and Pomasski as finding, however, that F. roseum Link and 
F. subulatum App. and Wr., which caused "intoxicating bread," dis- 
solved starch in the seeds of cereals. 

The writer has investigated the effect of F. discolor sulphur eum 
on starch, with results similar to those reported by Hawkins : starch 
grains in a rotted potato are intact, and stain as darkly with stronger 
iodine solutions as grains from normal potatoes. The appearance of 
less blue (more purplish or reddish) staining with dilute iodine is 
sometimes to be noted with starch from such rotted potatoes, and 
is of uncertain significance. On gelatinized starch, that is, starch 
paste made by boiling starch with distilled water, F. discolor sid- 
phureum and several other species of Fusarium grew fairly well and 
produced normal spores. It would seem, however, that, barring a pos- 
sibly less ready separation from the tissue, commercial starch should 
be procurable from dry rotted potatoes. 

To test the effect of prolonged action of fungi and bacteria caus- 
ing rot of potato tubers, a number of tubers seriously affected with 
F. discolor sulphureum were placed on March 1, 1918, in a jar, and 
this was covered and set away to allow the continued action of the 
Fusarium as well as any other organisms present. From time to time 



26 MINNESOTA BULLETIN 181 

samples were removed for examination of the starch grains, the mass 
being then stirred and set aside. The last examination was made 
December 24, 1918, at which time, after nearly 10 months of "rotting," 
the mass still contained entirely normal starch grains. Whether the 
number was reduced can not be stated, but no grains were found show- 
ing partial erosion. The rotting of potato tubers does not necessarily 
affect the starch present. Edson (15a) has recently published in some 
detail on this point. 

CROSS-INOCULATIONS 

Table V shows the results of some of the cross-inoculations at- 
tempted. The data are not presented unless the lesions produced 
were fairly definite. The rots reported were all obtained at room 
temperature. The plants inoculated were kept at a greenhouse tem- 
perature of about 18 to 24 degrees C. 

The evidence presented in Table V seems to indicate that various 
Fusaria may cause rot on certain fruits, such as cucumber, apple, or 
tomato, the host serving as hardly more than a "culture medium," 
in these cases, for the development of the Fusarium. Potato tubers 
may also be rotted by several species of Fusarium, altho it was found 
that with certain Fusaria, rot was obtained more readily after the 
potatoes had been dug some little time. Sprouting did not seem to be 
a necessary corollary. Such forms as F. trichothecioides and F. dis- 
color sidphureum, could of course produce rot at any time. While it is 
evident that certain forms, including those just noted, are, under nat- 
ural conditions, the chief producers of injury to potatoes, it is not 
apparent that any certain species of Fusarium causes rot on tomato, 
cucumber, and other vegetables. 

Cross-inoculation experiments are being continued, since it is evi- 
dent that the effect of Fusaria on different hosts is important from 
the standpoint of crop rotation. 



FUSARIUM DISEASES IN MINNESOTA 



27 



TABLE V 
Results of Cross Inoculations with Fusaria 









Extent of 




Fusarium 


Host tried 


Development 


injury 3 or 4 
weeks 


Remarks 


F. oxysporum 


Orange fruit 


Rot 


M fruit 






Tomato fruit 


Rot 


J-2 fruit 






Potato tuber 


Rot 


Whole tuber 


Usually a soft rot. 




Potato plants 
Cucumber fruits 


Injury 
Soft rot 




See previous data 










Apple Fruit 


Rot 


M fruit 






Bean plants 
Pea plants 


No effect noted 




Sterilized soil used 




Slight root in- 










jury 






F. discolor sulphureum 


Cucumber fruits 
Bean plants 


Soft rot 
No wilt or rot 
noted 


Yi fruit 


Abundant rot 

Light and heavy in- 










oculations made 




Pea plants 


No wilt or rot 
noted 




Light and heavy in- 










oculations made 




Potato plants 
Potato tuber 


No "wilt" 




See previous data 




Rot, usually 










dry rot 


Whole tuber 


See previous data 


F. trichothecioides 


Orange fruit 


Rather soft rot 


\i fruit 


Rind and core par- 
ticularly attacked 




Lemon fruit 


Rather soft rot 


\i fruit 






Apple fruit 


Rather soft rot 


Yi fruit 






Sweet potato 


Slight rot 


25mm 






Cucumber fruit 


Soft rot 


H fruit 






Tomato fruit 


Soft rot 


Yi fruit 






Carrot 


Dry rot 


Y± carrot 






Year old pota- 










to tuber 


Dry rot 


Yt tuber 






Newly dug po- 










tato 


Dry rot 


YL tuber 






Rotted potato 










tubers plant- 










ed 
Apple fruit 


No wilt 






F. eulmorum 


Slight rot 


30 mm 






Potato tuber 


Rather soft rot 




See previous data and 










Fig. 21 




Cucumber fruit 


Soft rot 


li fruit 






Bean plants 


No injury not- 
ed 








Pea plants 
Potato tuber 


No injury not- 
ed 
Rot in some 






Fusarium from bean 










cases 


25-40 mm 






Bean plant 
Pea plant 


Root rots 




See previous data 




Slight root in- 
jury 
Rot in some 






Fusarium from pea 


Potato tuber 










cases 


25-40 mm 






Pea plant 


Root rots anc 
wilt 








Bean plant 


Trace root in 
jury 




Injury occasional 


F. lini 


Potato tuber 


Some rot 


20-40 mm 






Cucumber fruit 


Rot 


M fruit 




F. lycopersici 


Cucumber fruit 


Rot 


Yi fruit 





28 MINNESOTA BULLETIN 181 

DOES THE SUBSTRATUM ALTER THE PATHOGENICITY 

OFFUSARIA? 

Carpenter (8) has reported several Fusaria as able to produce 
rot in potatoes. Sherbakoff (59, p. 100) noted that "Several series 
of inoculations of potato tubers showed (a) that a considerable num- 
ber of Fusaria can cause more or less rapid decay of the tubers, and 
(b) that most of the Fusaria readily produce rot only after the tubers 
begin to sprout." Wollenweber (76, p. 37) considered that in general 
the wilt parasite of one host was not found on living organs of another 
host, and that "the possibility of the adaptation of the parasite de- 
creases proportionately to the taxonomic distance of the host." He 
states, however, that "whether such [gradual to other hosts] adapta- 
tion occurs and causes changes in the nature of the parasite, indicated 
in pure culture by differences in general appearance, production of 
color, etc., has not been determined." Sherbakoff (1. c. p. 103) noted 
cases of possible mutations or fluctuations and of temporary changes 
in morphological characters. 

Sherbakoff also reported that he had isolated F. culmorum from 
rotted potato both alone and in association with other Fusaria. Wol- 
lenweber (1. c. p. 45) stated similarly that F. rubiginosum App. and 
Wr. (a probable synonym of F. culmorum) caused rot of potatoes at 
higher temperatures, but irregularly. The writer has isolated organ- 
isms similar morphologically to F. culmorum several times from rotted 
potatoes. In an endeavor to determine whether the morphological or 
physiological nature of these fungi might be altered by continued 
development on a host other than their characteristic habitat, inocu- 
lations were made with F. lini, F. culmorum, and the Fusaria men- 
tioned above as pathogenic to peas and to beans. Some rots of potato 
tubers were secured with all these forms, particularly with F. culmo- 
rum (see Figures 23 and 24). As yet these Fusaria have not been 
noticeably changed in morphology or pathology, but experiments 
should be continued for a much longer time. 

THE PRODUCTION OF "TOXIC SUBSTANCES" BY FUSARIA 

Lutz (35) has tested the effect of used nutrient solutions, includ- 
ing old Fusarium ("F. solani") solutions, upon the germination and 
development of certain fungi. He found that such fungi produced, 
after a period of growth upon a medium, substances which retarded 
the germination or growth of fungi grown subsequently in the same 
medium, even tho more nutrient substances were added; other fungi 
produced substances acting as accelerators rather than retarders. 



FUSARIUM DISEASES IN MINNESOTA 29 

Sometimes both types of substances were produced by the same fungus. 
The effect of these substances was usually destroyed by boiling, or even 
by lower temperatures. He was, however, unsuccessful in certain 
other attempts to demonstrate an enzymatic nature of these substances. 
Old Fusarium solutions which had been boiled and exposed to the light, 
allowed in general a larger growth of the fungus subsequently intro- 
duced than did the unheated solutions. He found also that for some 
of his used solutions, filtration through a clay filter removed the 
accelerating or retarding substances, altho this nitration did not alter 
the solutions in other instances. Lutz concludes that "Die von bestimm- 
ten Pilzen produzierten wachstumshemmenden resp. fordernden 
Stoffwechselprodukte, welche durch Kochen zerstort werden, haben 
keine spezifische Wirkung in dem Sinne dass sie immer nur auf Kei- 
mung und Wachstum derselben Pilzspezies Einfluss hatten ; sie zvirken 
auch auf die Sporen anderer Pilze." 

On Currie's (14) solution the writer grew F. oxysporum, F. dis- 
color sulphur eum, the Fusarium injurious to peas, Rhizopus nigricans, 
and other fungi. After the fungi grew for different periods of time, 
these solutions were filtered carefully through filter paper, since a clay 
filter may, according to Lutz, absorb the products in question. The 
results of preliminary germination tests made with spores of F. 
oxysporum and F. discolor sidphureum, agreed in general with Lutz's 
results, and indicated that substances were produced by these fungi 
which were inhibitory to the subsequent germination and early devel- 
opment of the two Fusaria in the same solution. Boiling the solutions 
destroyed this inhibitory action. 

Coons (13) reported work showing that F. oxysporum produced 
substances filterable through a Berkefeld filter, which caused early 
wilting of cuttings from potato vines when immersed in the filtered 
solution. Lathrop (31) found aldehydes to be produced by F. cubense 
E. F. Sm. Peltier (45) determined that a Botrytis produced a "harm- 
ful substance" that "may be some inorganic acid other than oxalic, or 
it may be a toxin of some kind, which, however, is not destroyed by 
heating to 100 degrees C." Graves (19) found that Rhizopus nigri- 
cans produced substances that exerted a negatively chemotropic effect 
upon the fungus greater than the positive chemotropic effect of certain 
food materials. 

The solutions mentioned above, on which the Fusaria and Rhizo- 
pus had grown in Erlenmeyer flasks closed with cotton plugs for 
different lengths of time, were filtered, and leaves of potato, coleus, 
ragweed, and other plants., all cut off under water, were introduced 
(Table VI). 



30 



MINNESOTA BULLETIN 181 



TABLE VI 
Effects of Solutions in Which Fungi Had Grown, on the Wilting of Excised Leaves 











Approximate 


Fungus which had 


Time of 


Treatment of solution 


Plant from 


time before 


grown in the solution 


growth in 


after filtration 


which leaves 


consp. 




solution 




were taken 


wilting 










Hours 


F. oxysporum 


2 months 


None 


Potato 


2* 


F. oxysporum 


2 months 


Boiled 


Potato 


2 


F. oxysporum 


2 months 


Diluted half with water 


Potato 


4 


F. oxysporum 


2 months 


Diluted and boiled 


Potato 


4 


F. oxysporum 


2 months 


None 


Coleus 


12 


F. oxysporum 


10 days 


None 


Potato 


24f 


F. oxysporum 


10 days 


None 


Lamb's 
quarters 


4t 


F. oxysporum 


42 days 


None 


Potato 


7 V 


F. oxysporum 


42 days 


Diluted half with water 


Potato 


8 


F. oxysporum 


42 days 


Filtered through diatoma- 










ceous earth 


Potato 


10 


F. oxysporum 


42 days 


None 


Ragweed 


7 


F. oxysporum 


42 days 


Diluted half with water 


Ragweed 


7 


F. oxysporum 


42 days 


Filtered through diatoma- 










ceous earth 


Ragweed 


8 


F. discolor sulphureum 


2 months 


None 


Potato 


2 


F. discolor sulphureum 


2 months 


Boiled 


Potato 


2 


F. discolor sulphureum 


42 days 


None 


Potato 


7 


F. discolor sulphureum 


42 days 


Boiled 


Potato 


8 


F. discolor sulphureum 


42 days 


None 


Ragweed 


6 


F. discolor sulphureum 


42 days 


Boiled 


Ragweed 


6 


Fusarium from pea 


2 months 


None 


Potato 


3 


Fusarium from pea 


2 months 


None 


Coleus 


12 


Fusarium from pea 


2 months 


Diluted half with water and 










neutralized 


Potato 


4 


Fusarium from pea 


2 months 


Diluted as above and boiled 


Potato 


4 


Fusarium from pea 


2 months 


Diluted with 3 vols, water 










and neutralized 


Potato 


4 


Fusarium from pea 


2 months 


Diluted as above and boiled 


Potato 


4 


Fusarium from pea 


42 days 


None 


Potato 


7 


Fusarium from pea 


42 days 


Made slightly alkaline 


Potato 


1% 


Fusarium from pea 


42 days 


Diluted with 3 vols, water 


Potato 


8 


Fusarium from pea 


42 days 


Boiled 


Potato 


7 


Fusarium from pea 


42 days 


None 


Ragweed 


4 


Fusarium from pea 


42 days 


Made slightly alkaline 


Ragweed 


4 


Fusarium from pea 


42 days 


Diluted with 3 vols, water 


Ragweed 


5 


Fusarium from pea 


42 days 


Boiled 


Ragweed 


3 


Rhizopus nigricans 


2 months 


None 


Potato 


04 


Rhizopus nigricans 


2 months 


None 


Coleus 


5 


Rhizopus nigricans 


42 days 


None 


Potato 


7 


Rhizopus nigricans 


42 days 


Boiled 


Potato 


6 


Rhizopus nigricans 


42 days 


Boiled 


Ragweed 


6 


Rhizopus nigricans 


42 days 


None 


Ragweed 


6 


None 


None 


Curries, freshly made 


Potato 


24 + 


None 


None 


Curries, freshly made, boiled 


Potato 


24 + 


None 


None 


Curries, 42 days old 


Potato 


16 


None 


None 


Curries, 42 days old 


Ragweed 


10 


None 


None 


Curries, 42 days old, boiled 


Potato 


14 


None 


None 


Curries, 42 days old, boiled 


Ragweed 


10 


None 


None 


Tap or distilled water 


Potato 


48 + 


None 


None 


Tap or distilled water 


Coleus 


48 + 


None 


None 


Tap or distilled water 


Ragweed 


24 + 



* Potato leaves for tests at any one time were taken from plants of the same age and in similar 
condition. For the two-months-old solutions, the leaves were from full-grown potato plants. 

t Tests after ten days reported in only this case, since with all the solutions it was evident 
that no particular development of "toxic substance" had ensued. 

t Wilt less pronounced than in preceding case. 



FUSARIUM DISEASES IN MINNESOTA 31 

Tests were also run with other Fusaria, and with Rhizoctonia and 
Penicillium. Wilting of excised leaves of various plants ensued more 
rapidly in old solutions. Wilting occurred even after considerable 
dilution. It is not to be explained on the basis of acidity. It is to be 
noted that no specific action is evident between the fungi tried and 
any one plant ; potato leaves wilt as readily in old Rhizopus solutions 
as in solutions in which F. oxysporum had grown. This is in agree- 
ment with Lutz's results in growing fungi in old solutions. A differ- 
ence exists, in that boiling the solution exerts no evident effect upon 
the action of old solutions on the leaves. In certain cases leaves 
took on a crinkled, distorted, or mosaic appearance, resembling some- 
times the condition obtained by Smith (62, pi. 63). 

"MIXED CULTURE" RELATIONSHIPS 

Nature seldom works with pure cultures. The interrelationships 
of various organisms forming the mixed cultures of nature have re- 
ceived little study (see Rahn 54, p. 181). In view of the frequency 
with which various bacteria may be associated with Fusaria in wilt 
diseases and tuber rots, the writer undertook tests to ascertain some 
relations between certain bacteria and Fusaria. 

It is a matter of common observation that fungi belonging to the 
genus Fusarium grow vigorously on any of the common culture media. 
Indeed, Fusaria are often troublesome as saprophytes in isolation, 
dilution, and other cultures of various organisms, on account of the 
vigor and rapidity of their growth. The writer has observed Fusaria 
to grow over and "swamp" colonies of Penicillium and other fungi. 

When, for example, two colonies of the same or of different fungi 
develop in a Petri dish, there is often a mutual cessation of growth 
at about the point where the colonies meet. Aside from the possible 
presence of any growth-arresting substance, there may be a lack of 
food, or possibly some mechanical obstruction of growth from the 
presence of hyphae, in the case of fungi. With a bacterial and fungous 
colony, however, the former should offer less mechanical impediment 
to the growth of the latter. 

Rahn (53) and others have shown that bacteria may produce 
growth-arresting substances, inhibiting more especially the further 
growth of the same organism. Elliot (16) has emphasized the changes 
in the mycelial characters of some species of Alternaria due to con- 
tact with colonies of certain bacteria. Sherbakoff (59, p. 214 f.) 
found chlamydospores especially abundant when Fusaria grew in the 
presence of bacteria. 



32 



MINNESOTA BULLETIN 181 



In the writer's experiments, Petri dishes of potato dextrose agar 
were used, inoculated at the center with the Fusarium, and midway 
on the radii with bacteria at the same time, then incubated until the 
colonies reached each other. In other cases the bacteria were first 
inoculated in the center and, since the Fusaria usually grow more 
rapidly than the bacteria, after incubation from one day to three days 
the Fusaria were inoculated on the radii. F. oxysporuvi, F. discolor 
sulphur eum, and the Fusaria from the bean and the pea were employed. 
Bacillus atrosepticus v. Hall, obtained through the courtesy of Dr. 
Morse, was used, since the blackleg organism is often found in both 
the stems and the tubers of potatoes. B. carotovorus Jones, certain 
undetermined species of bacteria isolated from rotted potato tubers 
and stems, Pseudomonas phaseoli E. F. Sm., and some common sapro- 
phytes such as Bacillus subtilis (Ehr.) Cohn and B. prodigiosus (Ehr.) 
Fleug., were also employed. Figures 25 to 30, with explanations in the 
list of plates, show in detail characteristic results. These experi- 
ments, which were duplicated several times, showed that in general 
a colony of bacteria which exerted a retarding influence on one species 
of Fusarium, exerted a similar influence on the other three species. 
Here again no specificity of "toxic substance" for any certain species 
of fungus was noted. Some bacteria exerted no observed influence, 
some accelerated, and some retarded growth of the fungus. The 
production of mycelium was sometimes changed in quantity, or the 
color reaction upon the medium was altered. On the whole the Fusaria 
were very tolerant to the presence of bacteria. No marked alteration 
of the mycelium or spores was found as a result of the action of the 
bacterial colonies on the fungus. While the writer has no reason to 
doubt the authenticity or vigor of the bacterial cultures used, he has 
not checked this point. Table VII summarizes the observations. 



TABLE VII 
Effect of Bacteria on Certain Fusaria 









From 


From 








Ps. 


rotted 


rotted 






Bacillus atrosepticus 


phaseoli 


potato 
stem 


seed 
piece 


B. subtilis 


F. oxysporum 


Slight alteration of growth; 


Retarded 


Retarded 


Retarded 






aerial mycelium marked 


growth 


growth 


growth 

medium 

colored 


No change 


F. discolor sul- 


No effect noted 


Retarded 


Retarded 


Marked 




phureum 




growth 


growth 


retardation 


No change 


F. from bean 


Growth somewhat accelerated, 


Retarded 


Retarded 


Retardation 


Acceleration* 




or no change* 


growth 


growth 




or no change 


F. from pea 


No effect noted 


Retarded 


Retarded 










growth 


growth 




No change 







• Acceleration of growth did not ensue in every trial, 
were secured in the different tests. 



In general, however, the same results 



FUSARIUM DISEASES IN MINNESOTA 33 

GENERAL DISCUSSION 

In considering Fusaria and the diseases they induce, we may first 
consider these fungi as vigorously growing saprophytes. Their longev- 
ity in the soil is a matter of prime importance. 

Bolley, in 1901 (5), showed that soil became "flax sick" because 
of an accumulation of F. lini; he stated that when once serious in the 
soil, "It can live from year to year upon the humus of the soil. . . . 
The fungus is able to live in the soil for many years without the 
presence of a flax crop to feed upon." Orton (40), referring to F. 
oxysporum in the San Joaquin Valley, California, stated that the fun- 
gus "may be present in nature in some of these alluvial soils" and at 
any rate soon accumulated sufficiently in the soil to render potato 
growing unprofitable. Jensen (26) reported the isolation of F. oxyspo- 
rum from soil from the eastern part of the United States. 

It is significant that Pratt (49,50,51,52) found F. trichotheci- 
oldes, F. radicicola, and apparently also F. oxysporum, in virgin west- 
ern soils. Werkenthin (74) found in Texas "that the virgin soil 
contained fungi which are known to be parasitic to cultivated plants, 
e.g., Fusarium Solani (Mart). Sacc, Fusarium oxysporum Schlecht., 
and Fusarium radicicola Wollenweber." These fungi he considered 
"true inhabitants of the soil." Taylor (68) found Fusarium spp. 
to a depth of 24 inches, in Rhode Island. Coons (13) obtained what 
was apparently F. oxysporum from native Michigan soils. 

There is evidence, then, that F. oxysporum may be present in 
many soils, and may become of considerable importance as succeed- 
ing crops of potatoes are grown; it must increase greatly from its 
growth in roots and stems of parasitized plants, and especially from 
its development on the dying potato stems and their debris. Such 
saprophytic fungi are able to withstand various unfavorable environ- 
mental conditions and persist in the soil through the production of 
microconidia and macroconidia, chlamydospores, or "perennating my- 
celium." In their growth, some Fusaria at least are able to compete 
successfully with various bacteria and other organisms with which 
they come in contact. 

While Fusaria are active saprophytes, there can be, on the other 
hand, no question as to their seriousness as plant parasites; their 
abundant saprophytic growth only renders their control in some re- 
spects more difficult. Despite their semi-parasitic nature, many Fu- 
saria, such as F. oxysporum, exhibit what amounts to a considerable 
specificity of parasitism to certain crops. F. oxysporum, however, 
can attack any part of the potato plant; stem, stolon, root, tuber, or 
even leaf. If the fungus is present in abundance, it can cause a com- 



34 MINNESOTA BULLETIN 181 

plete rotting off of the stems. It is not surprising, then, that from 
plants showing atypical symptoms of wilt in the field, F. oxysporum 
should be isolated, especially when the soil and weather conditions are 
propitious. The Early Ohio variety has been found to be commonly 
affected, particularly in the Red River Valley. This may be correlated 
with the fact that the Early Ohio remains through a considerable 
period in late summer in a condition of slow maturity and lessened 
vigor. 

In regard to the cause of wilting in potato plants into which 
F. oxysporum has gained entrance, a common explanation is that of 
mechanical vascular clogging. Link (35) considers the killing of 
the root system to be as important as this clogging, and Coons (13, 
p. 302) would add also the systemic poisoning from the production 
of substances by the fungus. The writer's experiments indicate that 
the fungus does produce toxic substances, but that various other fungi 
produce substances equally toxic, the only specificity being in the 
fact that the other fungi tried are ordinarily unable to gain entrance 
into the tissues of the plant. It would seem, however, that the three 
factors mentioned may operate together, with the addition in cases 
of foot rot of a considerable rotting of the underground portions of 
the potato plant. 

The association of injury to the potato stem from Rhizoctonia 
or Colletotrichum atromentarium (Berk. & Br.) Taub. (67) and of 
F. oxysporum within such stems, and the occasional coincident occur- 
rence of bacteria, Verticillium, or other fungi with F. oxysporum in- 
dicate that Fusarium wilt ensues more readily when the plant is weak- 
ened, and that other organisms may follow or aid the Fusarium in 
causing injury to the potato plant. 

Tisdale (70) has shown that the method of infection by F. lini 
is through root hairs, stomata, or epidermis; in resistant flax the 
plant was enabled to cork out the perhaps weakened hyphae, which 
could, however, gain preliminary entrance into the plant. He found 
further that F. conglutinans could penetrate the root hairs of flax, as it 
normally penetrated cabbage, but in flax it did not develop far. F. lini 
could also probably penetrate the young root hairs of cabbage. 

While rots of potato tubers are attainable in the laboratory with 
various Fusaria, in Minnesota the economically important Fusarium 
causing rot of tubers is, as far as the writer's evidence goes, F. dis- 
color sulphur eum. F. oxysporum may injure the tuber somewhat by 
development at the stem end or considerably in the vascular system, 
or occasionally by causing a rot ; other Fusaria more rarely cause dry 
rot alone or in association with other organisms. F. discolor sul- 
phureum evidently lives over especially in storage houses; the writer 



FUSARIUM DISEASES IN MINNESOTA 35 

has observed it in the fall growing luxuriantly, particularly on dirt 
floors and walls and on debris in potato houses that had held potatoes 
the previous year. 

Infection of the tuber may sometimes apparently ensue from con- 
tamination with the organism from the field. Once this fungus gains 
entrance it can develop at ordinary temperatures regardless of the 
humidity in storage, tho lower humidity obviously lessens the liability 
of infection. Relatively low temperatures, particularly cold storage, 
(1 to 3 degrees C.) allow but slight progress of the disease. 

While F. discolor sulpkureum ordinarily gains entrance through 
wounds, it is worthy of note as reported above that it may sometimes 
evidently infect through lenticels. Tn this connection it may be noted 
that Pratt (49) found that F. radicicola might infect the tuber through 
the stem end, lenticel, or eye; Wilcox, Link, and Pool (75) and Pratt 
(51) found that F. trichothecioides, on the other hand, infected only 
through bruises or other injury. Experiments and observations indi- 
cate that tubers become naturally infected with F. discolor sulpkureum 
principally through wounds. 

Tomato, cucumber, and some other fruits and various vegetables, 
especially when mature, may be rotted by several Fusaria. Num- 
erous other fungi, such as Peniciliium spp., may also rot these plant 
parts ; the action is hardly more than saprophytic growth upon easily 
available food material. While various fungi such as Peniciliium spp., 
Aspergillus spp., Stysanus stemonitis, Verticillium sp., Alternaria sp., 
are often found on or in rotted tubers or on healthy tubers, inoculation 
experiments failed to show any noteworthy ability of these fungi to 
rot the potato. The normal tuber is not an available source of food 
for them. Certain Fusaria are also unable to utilize readily the potato 
tuber as a food supply. 

CONTROL MEASURES 
POTATO WILT 
The methods of control ordinarily recommended are clipping the 
stem ends and rotation of crops. The former method, while of un- 
doubted value in removing some infection as well as the somewhat 
weaker eyes near the stem end, is not effective in seriously infected 
soils. Whether or not F. oxysporum occurs naturally in Minnesota 
soils, it is now widely distributed in the potato growing regions. Ob- 
servational evidence has failed to show that this fungus seriously 
attacks other crops in the state. It undoubtedly remains in some 
abundance in Minnesota soils for a considerable time. 



36 MINNESOTA BULLETIN 181 

It seems to the writer that the observation that the Fusarium 
causing potato wilt in Minnesota attacks the plants more especially at 
the time when blossoming, tuber setting, and hot weather have reduced 
the vigor of these plants, offers considerable hope in the development 
of control measures. From this standpoint the utilization of more 
vigorous strains of potatoes, rotation of crops, improvement of the 
seedbed, clean culture, and other factors tending to produce more 
vigorous plants likewise lessen the liability to attack by F. oxysporum. 

The writer is uncertain as to the interpretation to place upon the 
data presented by Manns (36, p. 317-319) and considered as tending 
to show that the "fungus will average in sick fields as great a percent- 
age in reduction under favorable conditions as under drouth." Manns 
evidently bases this conclusion on the fact that a three-year rotation 
plot at the Ohio station yielded in 1909 only 69 bushels per acre, 
whereas the county averaged 186 bushels per acre. It would seem, 
however, that throughout that county, in which the wilt had presum- 
ably been present previously (I.e., p. 311), it could not have greatly 
reduced the yield in 1909 despite the supposed higher percentage of 
seed infection in 1908 (I.e., p. 319; see also yield of spray plot, as 
noted below). Of course this does not explain the low yield in the 
rotation plot at the Ohio station in 1909. 

The work of Manns with bordeaux mixture is also significant. 
He found that despite the fact that "the only active factor at work 
in 1909 in reducing the yield on the area plotted for spraying was 
the work of the Fusarium blight, which was very prevalent . 
the growth in all sprayed plots continued from one to three weeks 
longer than in the unsprayed," with an average yield of 170.36 bushels 
per acre in the unsprayed and 181.72 bushels per acre in the sprayed 
plots. He adds, "The writer is satisfied that spraying heavily four 
times during the season does somewhat retard the action of the Fu- 
sarium fungus. Just how the results are brought about can not be 
satisfactorily explained." It would seem that the explanation may 
lie in the increased vitality of plants which are sprayed, and which 
can thus resist the action of the semi-parasitic F. oxysporum. Stew- 
art (66) had previously in New York State obtained a yield of 266 
bushels per acre from tubers obtained from wilted vines and in which 
"when cut at the stem end, blackened fibers are seen penetrating the 
flesh to a considerable distance." This plot was sprayed thoroly eight 
or nine times with bordeaux mixture. While it is not certain that 
Stewart was dealing with F. oxysporum wilt, the results obtained are 
comparable to those secured by Manns. 



FUSARIUM DISEASES IN MINNESOTA 37 

The writer has obtained as yet only empirical and fragmentary 
evidence as to the effect of spraying upon the occurrence of wilt in 
Minnesota. In the northeastern states, where spraying is commonly 
practiced, wilt is not prevalent. It must not be forgotten, however, 
that in this region cool weather and other conditions are more favor- 
able to the production of healthy and vigorous plants than in warmer 
regions. 

The results secured in Minnesota by A. G. Tolaas and certain 
county agents in the use of seed-plot methods, including selection, 
treatment, rotation, and good cultural conditions, indicate that wilt 
may be lessened by methods which tend to add vigor to the plants. 
A. G. Newhall, in 1918, found a case in point: A field in Cass County, 
a portion of which had received some care, had 15 per cent of wilt, 
whereas in another portion in which negligence had allowed weeds to 
develop and the potato plants to become less thrifty, 30 per cent of wilt 
occurred. 

Removal of debris from a field that had grown potatoes would 
lessen considerably the amount of culture medium for the Fusarium. 
The consideration involved as to fungi in returning such debris to the 
field after a period of rotting, is undetermined. 

POTATO DRY ROT 

Control measures that may be used against the rot caused by F. 
discolor sulphureum have not been found to be different from those 
recommended by various writers against other fusarial dry rots. 
Highly important is more careful handling of potatoes during and 
after digging to avoid cuts, bruises, and injuries, since the fungus 
attacks the tubers ordinarily and most easily through wounds. Stor- 
age cold enough to prevent absolutely the development of this rot 
is hardly attainable in any storage facilities possessed by the average 
grower, except possibly in the use of pits in the field. Considerably 
less infection would probably result, however, if the storage rooms 
were thoroly disinfected before potatoes were put in, and cleaned out 
carefully after the potatoes were removed. A disinfection of the 
tubers before storage would probably be commercially profitable, at 
least in the case of seed potatoes. 

Control measures against root rots of truck crops are indicated 
in the rotation of crops and the most favorable growing conditions 
for the crop. Careful handling and clean cool storage of fruits and 
vegetables subject to Fusarium rots will reduce the injury. 

SUMMARY 

1. Fusarium oxysporum Schl. is the cause of one of the most 
serious diseases of the potato plant in Minnesota. 



38 MINNESOTA BULLETIN 181 

2. This fungus characteristically produces the symptoms known 
as wilt. It attacks the roots and lower stem of the potato plant, 
particularly during the blossoming and tuber setting periods, when 
the weather is likely to be unfavorable to the potato, tho not to the 
fungus. F. oxysporum can moreover attack any part of the potato 
plant, and under certain conditions, particularly in wet soil, causes 
darkening and rotting of the stem and other symptoms not typical of 
wilt. It may rot the seed tuber under field conditions. 

3. As a saprophyte, F. oxysporum grows vigorously on the af- 
fected potato plants, accumulates in considerable abundance in the 
soil throughout the season, and persists for some time. In the fall 
it may attack plants which have previously produced a normal crop 
of tubers. 

4. The strains of F. oxysporum used were not, under ordinary 
conditions, sufficiently active parasites to cause infection of younger 
potato plants from artificial inoculations of the soil or seed tuber. 
At higher temperatures, symptoms of disease may occur. If the 
soil is inoculated heavily, rotting of the seed tuber and of the sprout 
or stem may result. 

5. Wilted plants do not necessarily result from planting seed 
tubers from affected plants. While such "seed" is less satisfactory 
than tubers produced under healthy vines, other measures in addition 
to seed selection or clipping off the stem ends are necessary to avoid 
wilt. 

6. While F. oxysporum is largely confined to the potato in Minne- 
sota, its habits are for the most part hemi-parasitic. 

7. The danger of serious infection by the wilt Fusarium is lessened 
by measures tending to add to the vigor of the plants, particularly 
during the latter part of the season. 

8. Fusarium discolor sulphur eum is the common cause of storage 
dry rot of potato tubers in Minnesota. 

9. This fungus gains entrance commonly through wounds, tho 
the rot may sometimes be induced by applying the fungus to the unin- 
jured surface of the tuber. 

10. Tubers from normal potato vines rot as readily as those 
from "constitutionally degenerate" plants, and as readily as tubers 
showing frost necrosis. None of the varieties of potatoes tested was 
found to be resistant to this tuber dry rot. 

11. Rot may develop on unsprouted tubers, and under dry condi- 
tions. Very slight rot may develop even at temperatures below 2 de- 
grees C. 



FUSARIUM DISEASES IN MINNESOTA 39 

12. At temperatures below about 16 degrees C, F. discolor sul- 
phureum produces more abundant aerial mycelium; at temperatures 
of from 20 to 30 degrees C, a dense pseudopionnotes. 

13. The starch grains in the tubers affected with dry rot are 
not appreciably affected. 

14. F. discolor sulpkureum does not naturally cause a wilt of 
potato plants, but infected seed tubers may produce less vigorous 
sprouts, or even no sprouts. 

15. While other Fusaria, such as F. oxysporum and F. culmorum 
may cause rot of potato tubers, such rots have been found to be of 
little economic importance in storage. 

16. Careful handling of tubers and the maintenance of clean 
cold storage conditions, are important prophylactic measures against 
the storage rot caused by F. discolor sulphureum. 

17. Fusarium root rots of Pisum sativum and of Phaseolus vul- 
garis are of importance in Minnesota. 

18. Ear rots of Zea mays due to Fusaria, probably including 
F. culmorum, are common in the state. 

19. Cross-inoculations indicate that wilt or root rot producing 
Fusaria may exhibit a selective tendency in their more common oc- 
currence on certain species of host plants, altho hemi-parasitic in that 
their action may be more distinctly influenced by conditions unfav- 
orable to the host. 

20. A temperature at which the host develops poorly may allow 
an active development of the attacking Fusarium. 

21. Isolations and cross-inoculations demonstrate that no single 
species of Fusarium is chiefly responsible for the common storage 
rots of vegetables and of cucumber and tomato fruits. 

22. Fusaria produced substances in old solutions that inhibited 
the germination of spores of the same or other fungi. After boiling, 
such old solutions allowed normal germination. 

23. Substances detrimental to such plants as potato, coleus, and 
ragweed, as shown by the wilting of excised leaves when placed in 
solutions, were also produced by Fusaria and other fungi in cultures. 
This injurious effect persisted after boiling, neutralization, or some 
dilution of the solutions. Specific fungi did not produce substances 
selectively injurious to any one or more plants. 

24. Fusaria are, in general, little influenced by bacteria, tho some 
bacteria may influence the rate of growth of Fusaria. 

25. The Fusaria examined could withstand considerable dessica- 
tion, exposure to low temperatures or to alternate freezing and thaw- 
ing, and can utilize a wide variety of food substances. Altho im- 
portant parasites, Fusaria are efficient saprophytes. 



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FUSARIUM DISEASES IN MINNESOTA 



41 



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42 MINNESOTA BULLETIN 181 

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FUSARIUM DISEASES IN MINNESOTA 43 

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EXPLANATION OF PLATES 

Figure 1. Plant showing typical wilting. Illustration by the courtesy of H. A. 
Edson of the United States Department of Agriculture. Taken in a field in 
Clay County, Minnesota, August 11, 1917. 

Figure 2. Rather early stage of wilting. Taken by Dr. Edson, also in Clay 
County, August 11, 1917. 

Figure 3. Plants collected August 23, 1918, from Clay County, illustrating the 
browning and rotting of the lower stems and of the roots. One plant also 
injured by stalk borer. Isolations yielded Fusarium oxysporum from these 
and similar plants. 

Figure 4. Plants showing similar and serious injury from foot rot, collected 
August 22 and 23, 1918, from Polk and Clay counties. The large plant illus- 
trates also the external production of fungus after having been in a damp 
place about two days. 

Figure 5. Tubers from plants showing foot rot, collected in Polk County, 
August 22, 1918. F. oxysporum and secondary fungi and bacteria present, 
causing a rather soft rot of the tubers. This rot was not ordinarily foul 
smelling. The blackening shows some tendency to follow the fibro-vascular 
bundles. 

Figure 6. Seed piece inoculated with F. oxysporum, received February 8, 1915, 
from W. A. Orton. (No. 3394 from Wollenweber's laboratory.) Inoculation 
September, 1917. The seed piece had rotted, the fungus was present in the 
stem. Reisolations yielded F. oxysporum. 

Figure 7. Cage heated by carbon electric lamps to secure higher temperature. 

Figure 8. Results of rather heavy inoculation of sterilized soil with F. oxy- 
sporum in the warmed cage. Seed piece rotted, one stem rotted off, other 
injured at the base. March, 1918. 

Figure 9. A case similar to Figure 8. Stems rotted off or seriously injured at 
the base. March, 1918. 

Figure 10. On the left, plant growing in the warm chamber in sterilized soil 
infected with F. oxysporum. Moist conditions did not allow a serious wilt- 
ing, but the plant is affected, particularly as indicated by the upper leaves. 
On the right, check grown from the same seed in sterilized soil. February, 
1918. 

Figure 11. Affected plant growing in artificially infected soil. The lower leaves 
have fallen and the plant is unthrifty. February, 1918. 

Figure 12. Surface view of tubers affected with F. discolor sulphureum from 
Beardsley. The wounds from which infection occurred can be seen on the 
surface. January, 1918. 

Figure 13. Longitudinal sections of the tubers shown in Figure 12. The rotted 
tissue is dark brown or blackish, containing some "pockets" filled with 
mycelium and sporodochia of the fungus. 

Figure 14. Stem and eye end infection of tubers from Clay County and char- 
acteristic of the rather early stage of a considerable infection in that region. 
Received December 10, 1917. 



46 MINNESOTA BULLETIN 181 

Figure 15. Effect of injury, moisture, and temperature on the development of 
rot by F. discolor sulphur cum. Figures A to E, inclusive, no injury to the 
surface; inoculum applied to the uninjured epidermis. Figures F, G, and H, 
slight injury to the surface before inoculation. Figures I to L, considerable 
wounding of surface previous to inoculation. Figures A and B, room tem- 
perature, damp. Figures C and D, room temperature, in a dessicator. 
Figure E, icebox (8 to 10 degrees C), damp. Figure F, room temperature, 
damp. Figure G, room temperature, dessicator. Figure H, icebox, damp. 
Figure I, room temperature, damp. Figure J, room temperature, dessicator. 
Figure K, room temperature and room humidity. Figure L, icebox, damp. 

Figure 16. Weak plant secured from planting seed partially rotted with F. dis- 
color sulphurcum. March, 1918. 

Figure 17. Healthy plant from seed tuber planted at same time as that of plant 
shown in Figure 16. Some rot on seed when planted. The rot did not, 
however, progress much. March, 1918. 

Figure 18. At left, base of plant shown in Figure 16, seed rotted; center, base 
of plant shown in Figure 17, seed healthy at insertion of stem. At right, 
another plant similar to the one on the left. March, 1918. 

Figure 19. Pea seeds rotted and roots and lower stems of young plants affected 
with Fusarium isolated from pea plants. 'Greenhouse inoculations, Sep- 
tember, 1917. 

Figure 20. Four tubers at left show slight rot, with F. discolor sulphurcum 
developed at 1.1 to 1.7 degrees C. Plugs cut out of potatoes in inoculating. 
The browned vascular ring in some of these tubers is due to frost necrosis, 
which had developed prior to the subjection to cold storage. Previous 
experiments demonstrated that this slight necrosis had no influence on the 
rate of rotting. At the right, a tuber almost wholly rotted when placed in 
cold storage. The rot progressed little at the temperature mentioned. This 
tuber was out before being put in cold storage and shows the development 
of some mycelium on the cut surface. Duration of experiment, 31 days, 
March 16 to April 16, 1918. 

Figure 21. Rot of potatoes from F. discolor sulphurcum at 8 to 10 degrees C., 
artificial inoculation, two weeks' development. 

Figure 22. F. discolor sulphurcum : center of plate, mycelium produced at 8 to 
10 degrees C. ; area of less abundant mycelium produced at room tempera- 
ture, containing many small sporodochia not shown clearly; circumference, 
mycelium produced again at 8 to 10 degrees C. 

Figure 23. At the right, tuber rot secured at 25 degrees C. with F. culmorum 
from wheat; at left, rot by same fungus at room temperature (about 18 to 
20 degrees C.). Time, two weeks. 

Figure 24. Rot started by F lint on potato tuber. Time, two weeks. 

Figure 25. F. oxysporum inoculated January 25, 1918, in the center. The 
stained area (dark red in natural color) shows the area occupied by a colony 
of bacteria obtained originally from a rotted seed piece and as yet unidenti- 
fied, over which the fungus grew slowly, as indicated by the lines marking 
dates. Opposite this a colony of Bacillus atrosepticus was present, but 
exerted no influence on growth or production of color. A colony of Asper- 
gillus at the margin opposite the stained area checked the growth of the 
Fusarium. View from lower face of Petri dish. 



FUSARIUM DISEASES IN MINNESOTA 47 

Figure 26. View from above, showing mycelium of F. oxysporum growing 
over a colony of B. subtilis : aerial mycelium marks the margin ; no pause 
in the growth. The radii, etc., on the opposite side are due possibly to 
shrinkage of the medium. 

Figure 27. F. discolor sulphur eum retarded by a colony of bacteria (the same 
species of bacteria mentioned for Figure 25, obtained, from a rotted seed 
tuber). The fungus eventually grew completely over this colony; the conidia 
and mycelium produced thereon appeared normal microscopically. Opposite, 
a colony of Bacillus atrosepticus had exerted no influence upon the growth. 
This figure illustrates the ample macroconidial production at room tempera- 
ture. View from above. 

Figure 28. Fusarium from bean plant. The irregular bacterial colony, checking 
growth somewhat, is Fscudomonas phaseoli. (The fungus finally grew en- 
tirely over this colony, but more slowly.) Opposite roundish colony is 
B. subtilis. The growth of the colony was noticeably accelerated when this 
colony was reached, just as the growth has been accelerated on the lower 
side, . where the fungus has pushed out over a colony of B. atrosepticus. 
"Growth arresting and accelerating" substances, are evidently produced. The 
organisms shown in Figures 25 to 28 grew on potato dextrose agar under a 
bell jar at room temperature. Inoculations January 25, 1918, photographs 
February 5, 1918. 

Figure 29. At right, relation between bacteria from a soft-rotted potato and 
(1) F. oxysporum, (2) F. discolor sulphur eum, (3) Fusarium from pea, (4) 
Fusarium from bean. Bacteria inoculated in center November 9, 1918, fungi 
inoculations November 12, photograph November 15. The growth of the 
fungi was somewhat retarded, and the bacteria tended to grow between the 
fungous colonies. At left, B. atrosepticus in center. Fusaria numbered as at 
right, inoculations and photographs same date. 

Figure 30. At right, B. subtilis in center, exerting little influence on the Fusaria. 
At left, a colony of bacteria isolated from a potato stem has diffused sub- 
stances through the medium checking equally the growth of the four Fusaria. 
Reciprocally, the bacterial colony ceased to enlarge. Inoculations in both 
plates : bacteria, November 9, 1918. Fusaria, November 14, photograph 
November 25. 







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